“Upgrade ready” on the website means you can finance a phone on your line. As you go through the upgrade process and select the device you want it’ll show available trade-in deals based on your plan. The Go5G Plus plans get the crazy discounts.Like trading in an old iPhone XR and getting $830 off the latest iPhone 14 series.

https://www.reddit.com/r/tmobile/comments/1469uw8/can_someone_please_explain_what_upgrade_ready/